In polarizing plates, which are assembled into display devices such as liquid crystal displays (LCD), and optical films, which are assembled into plasma displays (PDP), their outermost surfaces undergo a hard coat treatment to prevent damage, stains, etc., and as materials to be treated, materials with low surface energy or polarity are used. In addition, in PVA (polyvinyl alcohol) layer-protecting films that have recently been used in polarizing plates, triacetyl cellulose films have been replaced by norbornene resin films having low polarity.
For these reasons, in the case where optical films such as polarizing plates were pasted on display panels, conventional pressure-sensitive adhesive tapes had deficient adhesion reliability and caused problems in durability. As the usage of liquid crystal display devices becomes wider, they are used in various environments, and a high degree of adhesiveness, which does not cause peeling-off, is also in demand for pressure-sensitive adhesive tapes for pasting constitutional parts. In addition, high transparency is also required for the pressure-sensitive adhesive tapes so that the visibility of display panels is not lowered.
In Patent Documents 1 and 2, pressure-sensitive adhesive sheets (pressure-sensitive adhesive tapes) that are used for pasting optical members are presented. However, in pressure-sensitive adhesive compositions containing a lot of carboxyl groups, there has been a problem that adhesiveness becomes lowered with respect to an adherend having low polarity.
In addition, as a method for raising the adhesiveness to the adherend having low polarity, a method in which a tackifying resin (tackifier) is added to the pressure-sensitive adhesive compositions has been known. In Patent Documents 3 and 4, acrylic pressure-sensitive adhesive compositions, in which a rosin or hydrogenated tackifying resin is added as a tackifying resin to acrylic pressure-sensitive adhesive compositions, are presented. However, there still has been a case where the improvement of the adhesiveness to the adherend having low polarity could not be sufficiently achieved.    Patent Document 1: JP-A-2003-49128    Patent Document 2: JP-A-2005-298724    Patent Document 3: JP-A-6-207151    Patent Document 4: JP-T-11-504054